Thermoplastic adhesives, otherwise known as “hot melt” adhesives have been widely used in industry for adhering many types of products. Hot melt adhesive dispensing systems generally include a dispenser coupled with one or more dispensing guns, heated hoses connected to the guns, and a dispensing unit for melting and supplying heated liquid adhesive to the guns through the heated hoses. The dispensing unit of conventional hot melt adhesive systems include a tank, a heater, a pump, a manifold, and a controller. The heater is generally located in a base of the tank for melting and heating solid or semi-solid adhesive material received in the tank.
After the adhesive material is melted and heated in the tank, a pump coupled to the tank and the manifold pumps liquid adhesive from the tank, through the manifold and heated hoses to the dispensing guns. The controller controls the power supplied to the tank heater and heated hoses to maintain the liquid adhesive at an appropriate viscosity and temperature depending on the application. The controller also performs many other control operations of the system.
Conventional dispensing units further include a strainer which is loosely placed in the bottom of the tank to cover the tank outlet. The strainer prevents foreign objects in the adhesive flow from entering the pump and can be freely removed from the tank to permit cleaning of the tank. A drawback of this design is that operators occasionally neglect to replace the strainer after cleaning and prior to resuming operation of the hot melt system. This exposes the pump to potentially severe damage from foreign objects that may fall into the tank and get drawn into the pump. For at least this reason, a need exists for a more robust strainer design which prevents foreign objects from entering the pump and permits access to the tank for cleaning, yet which is failsafe to prevent operation without the strainer.
In some hot melt adhesive systems, the dispensing unit further includes an adhesive level indicator located in the tank interior. A shield is generally provided to protect the level indicator from damage by foreign objects or from being impacted by solid or semi-solid adhesive as it is deposited into the tank. An improved strainer that could also function as a shield for a level indicator would be an even more desired improvement over previous dispensing unit designs.